As one of conventional ultrasonic flow-meters of this type described above, there is known an ultrasonic flow-meter in which a passage is equally partitioned into a plurality of passages and an ultrasonic sonar is disposed in one of the partitioned passages (for example, see Patent Literature 1).
The conventional ultrasonic flow-meter will be described below with reference to FIG. 12. FIG. 12 is a cross-sectional view of the conventional ultrasonic flow-meter.
As illustrated in FIG. 12, conventional ultrasonic flow-meter 100 includes cylindrical basic passage 101, cylindrical honeycomb structural bodies 102 (passage partitioning members), circular mesh 103, and a pair of ultrasonic sonars 104. Cylindrical honeycomb structural bodies 102 are provided in cylindrical basic passage 101 and arranged to equally partition cylindrical basic passage 101 into a plurality of passages. Circular mesh 103 is disposed at a downstream side of cylindrical honeycomb structural bodies 102 of cylindrical basic passage 101 and rectifies a target fluid of cylindrical basic passage 101. The pair of ultrasonic sonars 104 are disposed near an inlet (at an upstream side) and an outlet (at a downstream side) of measurement passage 102A which is formed by at least one of cylindrical honeycomb structural bodies 102 of partitioned cylindrical basic passage 101.
With that arrangement, the flow of the target fluid flowing in cylindrical basic passage 101 is rectified to cancel deviation of the flow and prevent the flow from being turbulent. As a result, it is believed that the flow rate or the flow velocity of the target fluid can be measured accurately.
Further, Patent Literature 1 discloses not only the above described configuration of cylindrical basic passage 101 but also a configuration of partitioning a passage by providing a passage with a rectangular cross section and rectifying plates arranged at equal intervals and extending in parallel with a flow of the target fluid flowing through the passage.
However, the configuration of the conventional ultrasonic flow-meter is restricted in the arrangement such that the flow-meter needs to have respective partitioned cylindrical honeycomb structural bodies 102 (passage partitioning members) disposed evenly, so as to cause an average flow rate of the target fluid flowing through cylindrical basic passage 101 to flow in measurement passage 102A having the pair of ultrasonic sonars arranged inside.
In addition, since the conventional ultrasonic flow-meter needs to dispose members having large pressure losses such as the circular mesh at outlets of the cylindrical honeycomb structural bodies (passage partitioning members) to equalize the flow of the target fluid, a range of flow rate is problematically narrowed.    PTL 1: Unexamined Japanese Patent Publication No. 2003-185477